GaN HEMT and GaN MISFET devices have been used in the prior art. It is found, however, that such devices may have a certain degree of unreliability when the GaN epi material has high stress.
Typical gate metal, such as Ni/Au, produces a compressive stress on the GaN HEMTs operating at elevated channel temperatures. The compressive stress, which is a function of temperature, reduces carrier charge density in the device channel and can also generate a crack in the semiconductor material near the drain side of the gate edge, thereby shortening the device lifetime.
What is needed, therefore, are techniques to improve the reliability of such GaN devices.